This invention relates to apparatus and methods of electrostatography using a double-sleeved roller, and more particularly, to electrostatographic apparatus and methods of using a double-sleeved compliant roller, either as a primary image-forming member or as an intermediate transfer member for electrostatic transfer of toner images to receiver members.
The use of an intermediate transfer member in an electrostatographic machine to transfer toner from an imaging member to a receiver (e.g., paper) is well known and is practiced in commercial electrophotographic copiers and printers. A toner image formed on a primary image-forming member (PIFM) is transferred in a first transfer operation to an intermediate transfer member (ITM), and is subsequently transferred in a second transfer operation from the ITM to a receiver. In the second transfer of a toner image from an ITM roller to a receiver, a transfer back-up roller is commonly used behind a paper receiver, a nip being formed to press the receiver to the ITM.
As disclosed by Rimai et al., in U.S. Pat. No. 5,084,735 and Zaretsky and Gomes, in U.S. Pat. No. 5,370,961, use of a compliant ITM roller coated by a thick compliant layer and a relatively thin hard overcoat improves the quality of electrostatic toner transfer from an imaging member to a receiver, as compared to a non-compliant intermediate roller. Zaretsky, in U.S. Pat. No. 5,187,526, further discloses that electrostatic transfer can be improved by separately specifying the resistivity of the ITM roller and the transfer back-up roller. Bucks et al., in U.S. Pat. No. 5,701,567 disclose an ITM roller having electrodes embedded in a compliant blanket to spatially control the applied transfer electric field. Tombs and Benwood in published international Patent Application WO 98/04961 disclose the use of a compliant ITM roller in conjunction with a paper transport belt in a multi-color electrophotographic machine.
The use of a removable endless belt or tubular type of blanket on an intermediate roller has long been practiced in the offset lithographic printing industry, as recently disclosed by Gelinas in U.S. Pat. No. 5,894,796 wherein the tubular blanket may be made of materials including rubbers and plastics and may be reinforced by an inner layer of aluminum or other metal. As disclosed earlier, for example, by Julian in U.S. Pat. No. 4,144,812, an intermediate lithographic roller includes a portion having a slightly smaller diameter than the main body of the roller, such that a blanket member may be slid along this narrower portion until it reaches a location where a set of holes located in the roller allow a fluid under pressure, e.g., compressed air, to pass through the holes, thereby stretching the blanket member and allowing the entire blanket member to be slid onto the main body of the roller. After the blanket is located in a suitable position, the source of compressed air or fluid under pressure is turned off, thereby allowing the blanket member to relax to a condition of smaller strain, such strain being sufficient to cause the blanket member to snugly embrace the roller.
An intermediate transfer roller consisting of a rigid core and a removable, replaceable intermediate transfer blanket has been disclosed by Landa et al., in U.S. Pat. No. 5,335,054, and by Gazit et al., in U.S. Pat. No. 5,745,829, whereby the intermediate transfer blanket is fixedly and replaceably secured and attached to the core. The intermediate transfer blanket, disclosed for use in conjunction with a liquid developer for toning a primary image, consists of a substantially rectangular sheet mechanically held to the core by grippers. The core (or drum) has recesses where the grippers are located. It will be evident from U.S. Pat. No. 5,335,054 and U.S. Pat. No. 5,745,829 that owing to the presence of the recesses, the entire surface of the intermediate transfer drum cannot be utilized for transfer, which is a disadvantage requiring costly means to maintain a proper orientation of the useful part of the drum when transferring a toner image from a primary imaging member to the intermediate transfer roller, or, when transferring a toner image from the intermediate transfer roller to a receiver. Moreover, the fact that the blanket does not form a continuous covering of the entire core surface, owing to the fact that two of its edges are held by grippers, is similarly a disadvantage. Another disadvantage arises because there is inevitably a gap between these edges, so that contamination can become deposited there which may lead to transfer artifacts.
An electrostatographic imaging member in the form of a removable replaceable endless imaging belt on a rigid roller is disclosed by Yu et al., in U.S. Pat. No. 5,415,961. The electrostatographic imaging member is placed on the rigid roller and removed from the rigid roller by means involving stretching the endless imaging belt with a pressurized fluid.
Mammino et al., in U.S. Pat. No. 5,298,956 and U.S. Pat. No. 5,409,557, disclose a reinforced seamless intermediate transfer member that may be in the shape of a belt, sleeve, tube or roll and including a reinforcing member in an endless configuration having filler material and electrical property regulating material on, around or embedded in the reinforcing member. The reinforcing member may be made of metal, synthetic material or fibrous material, and has a tensile modulus ranging from about 400,000 to more than 1,000,000 psi (2.8 to more than 6.9 GPa). The intermediate transfer member has a thickness between 2 mils and about 7 mils, and a bulk resistivity less than about 1012 ohm-cm.
May and Tombs in U.S. Pat. No. 5,715,505 and U.S. Pat. No. 5,828,931 disclose a PIFM roller including a thick compliant blanket layer coated on a core member, the thick compliant blanket surrounded by a relatively thin concentric layer of a photoconductive material. The compliant primary imaging roller provides improved electrostatic transfer of a toner image directly to a receiver member. It is disclosed that the compliant imaging roller can be used bifunctionally, i.e., it may serve also as an intermediate member for electrostatic transfer of a toner image to a receiver. May and Tombs in U.S. Pat. No. 5,732,311 disclose a compliant electrographic PIFM roller. Disclosures in U.S. Pat. No. 5,715,505, U.S. Pat. No. 5,828,931 and U.S. Pat. No. 5,732,311 are hereby incorporated by reference.
U.S. patent application Ser. No. 09/574,775 filed on even date herewith in the names of M. F. Molaire et al. discloses a single-sleeved compliant PIFM roller and a method of making such roller. The sleeve is a photoconductive member, the sleeve resting on a compliant layer coated on a core member. This improves over U.S. Pat. No. 5,715,505 and U.S. Pat. No. 5,828,931, in that the coatings including the roller are made more reliably and more cheaply and also that the photoconductive sleeve may be readily removed and replaced when at the end of its useful life, thereby lowering cost and reducing downtime. It also provides an improvement over U.S. Pat. No. 5,415,961 by providing a core member having a thick compliant layer over which the sleeve member is placeable and removable.
A central member of a sleeved ITM including a thick compliant layer coated on a rigid core member, as disclosed in Molaire et al., is disadvantageously subject to damage of the compliant layer when removing or replacing a sleeve member. In some embodiments, the rigid core member is electrically biased to effect transfer of toner, and because the electrical properties of the compliant layer coated on the core member alter with age, typically becoming more resistive, the compliant layer has a finite lifetime requiring periodic replacement of the central member. A compliant layer on a rigid core of a sleeved PIFM, as disclosed in Molaire et al., may also be subject to damage when removing or replacing a photoconductive sleeve member.
An electrostatographic imaging member that includes a photoconductive drum that has inserted therein a compressible sleeve with the composite then being expanded to fit upon a rigid cylindrical core support is disclosed by Swain in U.S. Pat. No. 5,669,045. The preferred sleeve is a foam that provides substantially no interference fit with the photoconductive drum to facilitate insertion of the sleeve within the drum. However, a relatively large interference fit exists between the rigid core and the sleeve to compress the sleeve as it is expanded by an expandable core. The compression of the sleeve is sufficient to render the electrostatographic imaging member substantially rigid and substantially free from distortion. A problem with an imaging member of the type described by Swain is that the photoconductive drum is not separately removable from the sleeve without also removing the sleeve from the core, thereby subjecting the sleeve to possible damage.
There is a need, therefore, to provide improvements for sleeved electrostatographic rollers. In particular, for sleeved ITM and sleeved PIFM rollers there is a need to lower costs by reducing potential damage to roller members over which sleeve members must be moved during removal or replacement of sleeves. Moreover, when a central member includes a core member adhesively coated by a compliant layer (over which a sleeve member may be moved) the central member must be replaced when the compliant layer is no longer useful due to aging or inadvertent damage. Typically, the core member is an expensive, highly toleranced drum, and although the central member may be regenerated by removal of the compliant layer followed by a recoating operation, this tends to be difficult and costly, and thus there is need for improvement, especially to provide cost reduction.
The invention is directed to providing improved intermediate transfer members and improved primary image-forming members that may be employed in electrostatographic apparatus and method. An improved intermediate transfer member includes a double-sleeved roller further including a cylindrical rigid core member, a compliant inner sleeve member (ISM) in intimate nonadhesive contact with and surrounding the core member, and a compliant outer sleeve member (OSM) in intimate nonadhesive contact with and surrounding the inner sleeve member. An improved primary image-forming member is a double-sleeved roller including a cylindrical rigid core member, an inner compliant sleeve member in intimate nonadhesive contact with and surrounding the core member, and a photoconductive or electrographic outer compliant sleeve member in intimate nonadhesive contact with and surrounding the inner sleeve member. An inventive double-sleeved primary image-forming member may be used bifunctionally as an intermediate transfer member. Any single inner or outer sleeve member can easily and independently be replaced on account of wear or damage, or replaced when at the end of a predetermined operational life. An expensive, finely toleranced core member can thereby be retained for long operational usage with many generations of sleeve members. The invention allows removal or placement of an inner or outer sleeve member on a core member, such that the core member remains fixed to the electrostatographic apparatus in which it is mounted.
In accordance with the invention, there is provided a reproduction method including forming a toner image on a moving primary image-forming member (PIFM) which is a first double-sleeved roller including a rigid cylindrical core member, a replaceable removable compliant inner sleeve member (ISM) in nonadhesive intimate contact with and surrounding the core member, and a replaceable removable photoconductive outer sleeve member (OSM) in nonadhesive intimate contact with and surrounding the ISM; electrostatically transferring the toner image, from the PIFM to a counter-rotating intermediate transfer member (ITM) which is a second double-sleeved roller, in a first transfer nip width produced by a pressure contact between the PIFM and the ITM, an electric field urging the toner image from the PIFM to the ITM, wherein the ITM includes a rigid cylindrical core member, a compliant ISM in nonadhesive intimate contact with and surrounding the core member, and a compliant resistive OSM in nonadhesive intimate contact with and surrounding the ISM; providing a second transfer nip width in a transfer nip produced by a pressure applied between the ITM and a transfer roller; establishing an electric field between the ITM and the transfer roller; and advancing a receiver member into said second transfer nip to electrostatically transfer said toner image from the ITM to the receiver member.